As explained previously on the context page:
- The heat pump Coefficient Of Performance (COP) is reduced as the temperature of the cold sink is reduced; and
- The increased working temperature of photovoltaic solar collector reduces the photovoltaic conversion efficiency and its electric production.
As such, the project’s goal is to use a solar collector to increase the cold sink temperature, and in this way improve the heating performances of the heat pump. Hence, evacuating the heat from the solar collector will reduce its working temperature and improve its efficiency.
A new type of solar collector
In the recent years, the increased interest in solar energy reduced the manufacturing and installation cost of photovoltaic solar collectors. Researchers, engineers and architects have increased efforts to integrate solar collectors to buildings, and as a result the concept of “Building Integrated PhotoVoltaic” (BIPV) solar collectors was developed. In these systems, solar collectors improve the energy efficiency of buildings by reusing the parasitic heat produced by collectors during the conversion of sunlight to electricity. The concept of hybrid photovoltaic/thermal (PV/T) solar collectors where the collector can produce both electricity and heat was developed. In general, the photovoltaic (PV) plate is used as the solar absorber and a heat exchanger is bound on the back face of the PV plate. Then, different heat transfer fluids can be used. Air and water are generally the most popular. In our case, two phases carbon dioxide (CO2) will circulate in the heat exchanger and gather the heat from the photovoltaic cells. The following figure shows the hybrid solar evaporator prototype designed for this project.
Transcritical CO2 Heat Pump
Under this project, a prototype of a CO2 heat pump is being designed and built in order to test the system’s global performances. The heat pump will be running under a transcritical cycle. It means that the cycle is partly over and partly under the critical point of CO2 (i.e.: the critical temperature is around 31°C and the pressure around 7,377 kPa).
The following figure depicts the heat pump prototype.
Experimental Bench Test
One of the main objective of the project is to evaluate the performances and explore working problem that could arise with the use of this new solar collector. As a result, an experimental bench test is being developed to compare three different versions of the solar collector in real condition : a photovoltaic solar collector, a thermal solar collector and a hybrid photovoltaic/thermal solar collector. The following figure shows a 3D CAD of the setup used to compare the collectors.
The thermal and hybrid collectors both produce heat and are connected to the heat pump. Further, the PV and hybrid collectors both produce electricity and are connected to a constant electrical load. The solar PV collector is then used as a reference for the electrical production and the thermal one as a reference for the heat production. The experimental bench will assess whether the hybrid collector will be able to produce more energy than the other collectors for the same exposed area. Finally, the following figure shows the entire experimental bench test installed in Michel Trottier’s HelioLab on the roof of École de technologie supérieur (Montreal).